A semiconductor device typically contains a semiconductor chip that is mounted on a die attach pad, with a lead frame having a number of leads that extend inwards from the edges of the lead frame. During fabrication of the semiconductor device, electrical connections are established between bond pads on the semiconductor chip and predetermined ones of those leads. This is achieved through a wire bonding process in which one end of a wire is attached to each bond pad of the semiconductor chip and the other end of the wire to a point on the appropriate lead.
During the wire bonding process, strips of lead frames, in which the semiconductor chips are already mounted, are loaded into a magazine in a wire bonding apparatus. They are taken out of the magazine and positioned for wire bonding to take place in each lead frame. After the wire bonding process has been completed, the semiconductor devices are sent for further processing and packaging.
The wire used is usually of a small diameter. The bond pads are small and the leads are small. A clamping device is typically employed to hold the lead frame, more particularly to hold the leads of the lead frame down against a heater plate as the wire bonding process takes place. This is to ensure correct placement and efficient heat transfer. The structure of such clamps varies, but they include a clamp member to hold down the leads. The clamp member is held in position on a clamp post that is mounted in a clamp post holder. The holder in turn is securely mounted to the wire bonding apparatus.
Because the leads are small, the clamps have to be positioned accurately. Moreover, the clamps must ensure no gap between the lead frame and the heater plate. If that does not happen, the leads are not held down correctly and firmly, and the wire bonds may be poor. There is also the possibility that the clamp member may get in the way of the wire bonding.
To date, setting up the clamps has been a rather time consuming and inefficient process. The clamp member has been fixedly held in position on the clamp post. The clamp post has been fixedly held in position in the clamp post holder. The clamp post holder has been fixedly held in position on the wire bonding apparatus. There has been no means of adjustment beyond changing the height of the clamp post holder and thereby the clamp member by putting shims between the clamp post holder and the wire bonding apparatus. However, it takes trial and error to get the appropriate thickness. Thus, each time the clamp post holder has to be dismounted and re-tightened. This means that the calibration process is very time consuming and annoying, especially if no thickness of available shims will provide exactly the thickness required.